Filtration assemblies of the industrial type find usage in wide range of application areas including irrigation, cooling towers, fish farms, power generation plants, sea water treatment systems, steel industry, ships, and other areas supplying any liquid from a source to a system such as supplying of water from a source for industrial or domestic use. These filters mostly accommodate a rigid hollow filter inside a tubular body which normally suffers of clogging problems after a certain time of operation due to the small particles and larger substances coming through the liquid. Therefore, these filters are expected to clean themselves periodically according to predetermined parameters such as pressure drop through the filter, or otherwise are cleaned manually by labour which is cumbersome and not feasible in the plants of industrial scale.
Therefore, there are proposed various types of filters in prior art for screening of the micro- and macro-particles from a stream of liquid. EP-A-2 325 081, for instance, discloses a ballast water treatment device including a filtering unit of the above type for treatment of the ballasting water used in the ships. The filtering unit comprises a filter in a filter body which is equipped with an automatic washing unit with plurality of nozzles. In this system, said washing unit is located within the inner volume defined by the tubular filter and is activated by the sensors depending on the pressure drop caused by clogging of the filter surface. This system, however has drawbacks in many aspects such that the nozzles have the very limited capacity to suck and remove coarse particles and substances such as fishes, algae and wastes. More importantly, these kind of screening systems are not sufficient for filtering out both the fine and coarse particles within the very same system, and therefore require additional installations such as additional filtering units designed for the purpose of non-filtrated substances.
A further arrangement disclosed in document KR-A-20130063563 suggests a filtering unit working with the reverse principles such that liquid is filtered from outside through the inner volume of cylindrical filter whereby scratching devices with water jets are provided upon the filter. Thereby the dirtiness accumulated on peripheral surface of the filter is scratched with the help of pressurized water sprayed on the filter in a cleaning cycle. This system is again non-responsive to the drawbacks mentioned above, and is also complicated and disadvantageous because the scratching tools may deteriorate the filter surface.
DE-C-935 424 discloses a filter device enabling back washing, comprising two concentrically formed filters of unknown screen openings whereby the outer screen is arranged rotatable while the inner screen is fixedly placed, but is optionally arranged as liftable. Cleaning of the filter screens is carried out by using arrays of nozzles (h1, h2) applying pressurized liquid or gas, and removal of the dirtiness from the filter surfaces is carried out through a valve (k) and manifold (g) with the help of gravity.
As shown with the pertinent prior art scrutinized above, the conventional filters are designed for a particular mode of screening for a targeted range of particles or substances, and do not allow to carry out a second mode of screening for particles of a different magnitude. The importance of filtering in different modes gains importance in recent years because of the increased pollution in water sources and sea. To solve these problems, the conventional approach is to use different filtering units in series accommodating filters of different types for separately filtering out small and larger particles. This approach not only increases the costs and complexity of the overall system but is also disadvantageous in other aspects such that the liquid coming from the outlet of one filtering unit needs then be directed to the other filtering unit possibly with at least one 90° elbow conduit which affects the energy consumption for pumping of the liquid in the system because of the increased head loss. Adding onto this, the energy consumption associated with the second filtering unit, the overall operational costs dramatically increase in the conventional systems.
Therefore, an object of the present invention is to provide a filtration assembly which is capable of carrying out two different modes of screening for small and larger particles in situ.
Another object of the present invention is to decrease installation requirements for gradual filtration of fine and coarse particles in a filtration system.
Still a further object of the present invention is to provide a filtration assembly which has reduced costs and energy consumption as well as reduced head loss as compared to the state of the art filtering systems using of different filtering units for different modes of screening.
These and other objects of the present invention are achieved through the novel filtration system as disclosed in the appended claims.